1. Field of the Invention
This invention relates to a transparent coating member to be mounted on a light-emitting diode (hereinafter, xe2x80x9cLEDxe2x80x9d) and a light source for changing the color of a light emitted from an LED by mounting the coating member on the LED or forming a coating layer containing a fluorescent substance on the surface of the LED.
2. Discussion of the Related Art
As well-known, the LED is a crystal body having a p-n junction. Upon the application of a forward voltage, electrons are injected from the n region to the p-n junction and holes are injected from p region to the p-n junction. A light is emitted when the electrons and holes are recombined. Accordingly, free electrons are combined and energy released during this recombination is radiated as a light. Thus, there exist LEDs of limited colors. In other words, LEDs having a red LED chip emit only a red light; LEDs having a green LED chip emit only a green light; and LEDs having a blue LED chip emit only a blue light.
However, there has recently been a large demand for LEDs capable of changing a light emitted therefrom in order to meet multi-purpose applications. A color changing method for meeting such a demand is, for example, such that a suitable combination of red, green and blue LED chips are set in the LED and the color of the light emitted from the LED is changed by causing a different combination of chips to emit light.
Such an LED results in a complicated constructional design since four terminals: three different anode terminals of the red, green and blue LED chips and a cathode terminal, are necessary. The most fatal problem is that, since three different chips are set in the LED, a color balance is lost if any one of the chips is broken, with the result that a desired color cannot be obtained.
Further, in recent years, a white LED lamp has been proposed in which a layer of YAG (yttrium aluminate) fluophor is provided on a blue LED chip (Nikkei Sangyo Shinbun, Sep. 13, 1991 issue). This white LED lamp is designed to generate a white light by a light excited by the layer of fluophor and the afterglow of the blue LED chip. If a cap or a sheet containing a coloring agent is mounted on such a white LED lamp, a light of a desired color can be obtained.
However, the above white LED lamp has various problems that a high degree of application technique is required due to only a very small amount of fluorescent substance on the blue LED chip, a large variation of the color caused by a slight error and the application of a fine amount, and a price per lamp is very expensive.
The present invention has been developed as a result of studies to solve the above-mentioned various problems and an object thereof is to provide a transparent coating member for a LED which can easily change the color of a light emitted therefrom to a desired color.
It is another object of the present invention to provide a fluorescent color light source which can easily change the color of a light irradiated therefrom and diffuse the light of a stable color at a high luminance and is easy to maintain and inexpensive.
The invention is directed to a transparent coating member mountable on a light-emitting diode, comprising a fluorescent substance.
The invention is also directed to a fluorescent color light source comprising a light-emitting diode, and a transparent coating portion on the light-emitting diode, the transparent coating portion including a fluorescent substance.
The wavelength of emitted light peculiar to the light-emitting diode is changed by the fluorescent substance contained in the coating portion to change the luminescent color.
On the other hand, it is in reality very difficult to produce LEDs of uniform quality, and the color and luminance of the produced LEDs unavoidably vary. It is a very important problem how such variations can be suppressed without increasing production costs. Up to now, the variations have not yet sufficiently been suppressed.
Furthermore, when a blue LED tip coated with a cap including a fluorescent material is illuminated, there likely occurs a color variation between a lead end and a side surface. In general, the lead end portion becomes blue and the side portion becomes yellow. This phenomenon becomes more significant when the amount of fluorescent materials is reduced.
In addition, the cost of a fluorescent material is dominates the entire cost of a cap used to cover an LED and it thus is essential to reduce the amount of fluorescent material as much as possible.
Moreover, a transparent coating member used for an LED tip may be used in a dark room and it thus is appreciated to have an afterglow on after the light of LED is turned off.
In order to reduce color variation at a location of the transparent coating member, a transparent coating member having a lead end and a side surface mountable on a light-emitting diode (LED) according to this invention comprises a fluorescent substance and a light diffusion substance (LDS).
With the thus constructed transparent coating member, it becomes possible to reduce the color variation between the lead end and the side end surface of the transparent coating member when an LED enclosed therein emits light. At the same time, it was found possible to maintain the same level of chromaticity without significantly lowering luminance by using a reduced amount of fluorescent material and by adding a specific amount of light diffusion substance in the coating member. In short, addition of the light diffusing substance enables a reduction of color variation between positions of the transparent coating member covering an LED tip and a reduction of the amount of fluorescent material.
Another structure of a transparent coating member according to this invention comprises a fluorescent substance and a light storing pigment.
With the above construction, the transparent coating member shows an afterglow on and after turning off the LED enclosed in the coating member. This enables a user to locate the position of the coating member easily after turning off the LED in a dark room.
Yet, another construction of a transparent covering member having an inner surface and an outer surface according to this invention is a molded product that was formed in an upper mold and a lower mold where either one or both of an inner recessed portion of the upper mold and an outer projected portion of the lower mold (which is fit into the inner recessed portion of the upper mold) have their surfaces modified by a sand blasting process.
With the sand blasting process applied to either or both of the inner and outer surfaces of the molds (upper mold and lower mold), the transparent covering member formed from such a mold includes properties that enable a reduction of color variation and a luminance variation between the lead end and the side surface of the LED.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.